A stricter requirement was imposed on the safety and reliability of industrial and civil power supply along with the development of technology. According to some related national standards, a better EMC capability shall be provided by the low voltage electrical equipments and the power supply lines. In view of this technical tendency and development, a new design of residual current device which provides better protection to user and connected equipments is necessary.
An ordinary circuit breaker, such as MCB, usually has a mechanism of overload protection and short circuit protection. Different from the ordinary circuit breaker, a residual current device (RCD) has a mechanism for residual current protection besides from the overload protection and short circuit protection. The RCD detects residual current in the power supply line and then compares the detected current value with a pre-determined residual current threshold. The RCD disconnects the protected power line when the detected value is higher than the pre-determined value, in order to prevent the user and electrical equipments from being destroyed by the residual current.
Specifically, a RCD operates by measuring the current balance between two power lines, e.g., a live wire and a neutral wire, using a differential current transformer. It measures the values of the current flowing out the live wire and the current returning through the neutral wire. If the values of input and output current do not sum to zero, there is a leakage of current to ground or to another circuit, and the device will activate its residual current protection mechanism and break its electrical contacts.
A typical electronic RCD includes an operating mechanism for breaking and closing the contacts of power lines, a magnetic releasing unit, a heat releasing unit, a zero sequence transformer, a magnet, an electronic circuit and a housing for enclosing all the components. In the existing RCD, every component only implements its task for a single purpose besides acting as a current carrier. The single-purpose component design used in the existing devices makes the structure thereof less complicate and easy to manufacture. On the other hand, the assembling procedure of existing device is quite complicate, low efficient, unreliable and risky due to the huge amount of single purpose components needed by the device. Moreover, it was also found that the existing RCD does not have a good performance of arc extinguishing, and it is also vulnerable to the influence from surge voltages occurred on power lines.
In order to solve the problems of the existing RCD, the RCD proposed in present invention adopts a newly designed component with multi-purposes. The proposed RCD also improves the performance of arc extinguishing and anti-surge voltage.